1. Field of the Invention
The present invention relates to an optical information recording medium and a method for recording optical information.
2. Description of the Related Art
Optical recording media have recently come into wide use as a viable means for the storage and/or archiving of large volumes of information. In these systems, the optical recording materials undergo a localized change in optical properties such as absorption maxima or extinction coefficients when exposed to radiation of high energy density such as laser light. The localized change can be utilized for recording information.
A variety of optical recording materials have been developed. A conventional `write-once` blank disk (CD-WORM or CD-R) is coated with a dye, as a recording material, and solid state lasers are conventionally used to record as well as read the information. Since the lasers generally have emission wavelengths of about 770-790 nanometers, conventional recording media typically operate in these laser wavelengths.
In optical recording media, the trend is toward higher information density to accommodate a greater volume of stored information. Accordingly, it is conceivable for laser light to have shorter wavelengths to meet the requirements of recording and reading out the higher volume of information data. Currently, no optical recording materials adequately fulfill the requirements.
Various recording materials for CD-R recording media have been disclosed, for example, cyanine dye materials and phthalocyanine dye materials.
Disclosures on the cyanine dye materials, for example, are found in Japanese Laid-Open Patent Applications Nos. 57-82093, 58-56892, 58-112790, 58-114989, 59-85791, 60-83236, 60-89842, and 61-25886. Disclosures on the phthalocyanine dye materials are found in Japanese Laid-Open Patent Applications Nos. 61-150243, 61-177287, 61-154888, 61-246091, 62-39286, 63-37791, and 63-39888.
The above-disclosed dye materials, however, do not possess satisfactory light resistance or archival stability, and are not capable of recording and reading out with laser light having wavelengths shorter than 700 nanometers. Therefore, there remains a need for improved optical recording materials that are capable of recording and reading out with shorter wavelength laser light, and have adequate light resistance and stability characteristics.
Conventional disk apparatus for CD-R media recording and readout use lasers with wavelengths ranging from about 770 to 790 nanometers. To meet the requirements of recording and reading out higher volumes of information data, laser beams having shorter wavelengths will inevitably be required for CD-R systems.
In this context, it is noteworthy to add that conventional CD's and CD-ROM's (read-only-memory CD's) record information as pits on the surface of a substrate, and an aluminum reflecting coating is provided over the substrate and the pits. Since the aluminum layer has relatively few reflectivity changes with light wavelength, readout of recorded data appears feasible at the above-mentioned shorter laser wavelengths of future systems, as well as at wavelengths of conventional systems that are presently available. However, in contrast to the above-described aluminum layer, the recording media of CD-R may be considerably affected by the shorter wavelengths. Conventional CD-R media employ recording materials such as dye compounds that have their maximum absorption at wavelengths ranging from about 680 to 750 nanometers, and are designed to optimize parameters such as optical constants and layer thickness of constituent layers to exhibit high reflectivities at wavelengths of about 770 to 790 nanometers.
Accordingly, lower reflectivities of conventional recording media are typically observed at wavelengths shorter than 700 nanometers, which may give rise to shortcomings in future CD-R systems. As a result, information that is otherwise successfully recorded and read by the current CD-R systems, may be inadequately read by future CD-R systems.
Various CD-R media have been developed that include recording layers having a cyanine dye/metal reflecting layer construction (disclosed in, for example, Japanese Laid-Open Patent Applications Nos. 1-159842, 2-42652, 2-13656, and 2-168446), phthalocyanine dye/metal reflecting layer (Japanese Laid-Open Patent Applications Nos. 1-176585, 3-215466, 4-113886, 4-226390, 5-1272, 5-171052, 5-116456, 5-69860, and 5-139044), or a metal chelated azo compound/metal reflecting layer construction (Japanese Laid-Open Patent Applications Nos. 4-46186, 4-141489, 4-361088, and 5-279580). However, in the recording media fabricated from these dye materials, the optical characteristics are not satisfying at wavelengths shorter than 700 nanometers.
It is therefore very desirable to provide materials for recording media which satisfy the above-mentioned requirements.